In Python, global variables are variables declared outside of any function. This means they have a scope that encompasses the entire program, unlike local variables defined within functions.
Accessing and Modifying Global Variables
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Reading: You can access a global variable from anywhere in your program, including inside and outside functions.
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Modifying: To modify a global variable inside a function, you need to explicitly declare it as global using the global keyword. This tells Python to use the existing global variable rather than creating a new local one with the same name.
Example 1: Reading a Global Variable
Example of using or reading a global variable
# Global variable declared outside the function
count = 0
def increment_count():
# Accessing the global variable `count`
print("Current count (before):", count)
count += 1
increment_count()
print("Current count (after):", count)
Explanation:
⯌ count is declared as a global variable outside the function.
⯌ The increment_count function reads the value of count and prints it.
⯌ The function doesn't modify count directly.
⯌ Outside the function, the updated value of count (after the function execution) is printed.
Example 2: Modifying a Global Variable (Using global keyword)
Example of modifying a Global Variable (Using global keyword)
# Global variable declared outside the function
user_name = ""
def set_user_name(name):
global user_name # Declare `user_name` as global
user_name = name
set_user_name("Alice")
print("User name:", user_name)
Output
User name: Alice
Explanation:
⯌ user_name is declared globally.
⯌ The set_user_name function takes a name as input.
⯌ Inside the function, we use global user_name to modify the existing global variable.
⯌ The function assigns the provided name to user_name.
⯌ Outside the function, the updated value of user_name is printed.
Cautions with Global Variables
Excessive use of global variables can make code harder to understand and maintain. It's generally recommended to use local variables and function arguments whenever possible.
Modifying global variables within functions can lead to unexpected side effects if not handled carefully.
Alternatives to Global Variables
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Function Arguments: Pass necessary data as arguments to functions instead of relying on global variables.
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Class Variables: If a variable needs to be shared across multiple functions within a class, consider using class variables.
By understanding these concepts, you can effectively use global variables when necessary while prioritizing local variables and function arguments for cleaner and more maintainable code.
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